Sudden Death in Infants is ill-understood and presently tends to be attributed to malfunction of the nervous system. The hypothesis that a mechanical defect in the maturation of larynx may be involved is proposed for study. The gross anatomy of the larynx at birth differs substantially from the adult, but the stages of maturation of the morphological structures and of their mechanical modes of functioning have not been specified. The material for this investigation will be drawn from victims of the Sudden Infant Death Syndrome and from a parallel series of deaths due to other causes in the first year of life, in order to define the major developmental horizons throughout infancy. The force-deformation characteristics of the various elastic structures at the entrance of the larynx will be measured in autopsy specimens. The defining equations will be programmed into a PDP-15 computer in order to explore the dynamic state of these elements in a closed larynx and to quantify critical perturbations. Some entire specimens will be subjected to serial section and x20 photographic enlargements will be used as the basis for re- constructions in which the relation between anatomical measurement and elastic behavior will be studied. The maturation of mechanics of the larynx will be observed in living animals, beginning with beagle puppies, by means of x-ray techniques after application of tantalum powder markers at strategic points on the laryngeal cartilages, and by fiberoptic cine- laryngoscopy.